Seawalls

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Contents

Introduction

Seawalls are vertical or near vertical shore-parallel structures designed to prevent upland erosion and storm surge flooding. Seawalls are generally massive concrete structures emplaced along a considerable stretch of shoreline at urban beaches. The term "sea wall" is commonly used to describe a variety of shoreline armoring structures including revetments.

History

For as long as humans have lived along coastlines, they have made attempts to mitigate the effects of erosion and tame or defend against the natural elements to improve the safety of their homes and other buildings. The history of seawalls dates back thousands of years. Shorelines provide many advantages to cultures and societies, serving as abundant food sources with fish, crab, clams and other sea creatures, as well as providing access to transportation and shipping to and from distant lands via the natural highways which are the world's oceans.

Constantinople

The original city of Byzantium had seawalls, some traces of which still survive.[1] and are usually attributed to Constantine I, but the first written references to seawalls come hundreds of years later in 439, when the urban prefect Cyrus of Panopolis was ordered to repair the city walls and complete them on the seaward side.[2] This was done primarily as a defense against invading tribes such as the Vandals, who conquered Carthage in that same year, but cities built along shorelines sought defense from natural as well as human threats.

Pondicherry

The city of Pondicherry in India is protected by a seawall which stretches 2 kilometers along its coastline. First completed by the French in 1735, the Pondicherry seawall reaches a height of 27 feet above sea level. A weather-beaten cement plaque with the year 1952 is still visible along a section of the seawall. The seawall is protected from the direct onslaught of waves by rows of granite boulders which are reinforced every year to stop erosion. Whenever gaps appear or the stones sink into the sand, the Government adds more boulders to keep it strong. When a 24-foot high tsunami caused by the Indian Ocean earthquake of 2004 struck Pondicherry, the city's center stayed dry and casualties were limited to about 600, most of whom were in villages outside the protective barrier.

Impacts of Seawalls on Beaches

  1. Passive erosion - "Wherever a hard structure is built along a shoreline undergoing long-term net erosion, the shoreline will eventually migrate landward beyond the structure. The effect of this migration will be the gradual loss of beach in front of the seawall or revetment as the water deepens and the shoreface moves landward.... While private structures may be temporarily saved, the public beach is lost. This process of passive erosion appears to be a generally agreed upon result of fixing the position of the shoreline on an otherwise eroding stretch of coast, and is independent of the type of seawall constructed." It is evident that passive erosion will eventually destroy the recreational beach area unless this area is continually replenished. Excessive passive erosion may impact the beach profile such that shallow areas required to create breaking waves for surfing are lost.
  2. Placement loss - Seawalls are placed on the beach. In many cases, construction of seawalls is on public property (beach). An example is in Solana Beach, California, where most land for seawalls is leased free of charge to the property owners. This is a taking of extremely valuable public property.
  3. Active Erosion - Refers to the interrelationship between wall and beach whereby due to wave reflection, storm surf zone narrowing and a thousand other processes the wall may actually increase the rate of loss of beach. This is site specific and dependent on sand input. There are varying opinions on if this effect actually exists. However, as watchdogs of the coast, until there is overwhelming evidence that this effect is not significant, many of us have opposed seawalls on this basis.
  4. Public access impacts - these can be a result of passive erosion, placement loss or active erosion. Seawalls built on eroding beaches will lead to the loss of access. Solana Beach and many other areas of North San Diego County beaches are eroding.
  5. Visual/aesthetic impacts - Seawalls are ugly and detract from simple pleasures as a walk on the beach.
  6. Economic issues - local, state or federal subsidies or construction to protect private property, or insurance coverage. Construction is performed on State or Municipal land. The public has never been compensated for this loss of valuable property.
  7. Loss of sand supplied by eroding bluffs that are armored. A minimal fee for this sand is collected from property owners for the sand that would provide beach material. Additionally, the eroded area would create a beach. We do not feel the public is sufficiently mitigated for the loss of sand and beach.
  8. The most important thing to remember is that a seawall is never built to protect the beach. Rather, it is built to protect property, structures or a cliff from erosion.


Our Position

Beach Preservation Policy

Ratified by Surfrider Foundation Board of Directors, April 17, 1999

Introduction: The Surfrider Foundation recognizes that beaches are unique coastal environments with ecological, recreational and economic value. The Surfrider Foundation further recognizes that beaches are a public resource and should be held in the public trust. As human activities and development in coastal areas increase, the need for preservation of beaches becomes ever more apparent.

"Hazards" occur when naturally dynamic coastal processes encounter static human development, and when humans interfere with marine and littoral systems. The Surfrider Foundation is working proactively to promote conservation and responsible coastal management that avoid creation of coastal hazards or erosion problems. The Surfrider Foundation supports coastal research and science-based management of coastal resources to promote sustainable, long term planning and preservation of beach environments.

This policy is general in nature; the Surfrider Foundation recognizes that every specific case must be evaluated in the context of its local setting. Whereas: Beaches are often perceived as separate habitats, but in reality are small parts of much larger coastal ecosystems. These systems include watersheds, wetlands, and nearshore marine environments.

Beaches are dynamic in nature and change on multiple temporal and spatial scales. These changes are therefore difficult to predict with certainty.

Therefore: The Surfrider Foundation hereby advocates actions to promote long term beach preservation for the benefit of the public. Coastal areas that are free of development should be protected via proactive means that do not interrupt coastal processes. These include:

  • Placement of beaches and beachfront lands in public trust
  • Establishment of beach setbacks based on current and historical erosional trends
  • Restoration of natural sediment transport processes in coastal watersheds


In areas where erosion threatens existing coastal development, the Surfrider Foundation advocates appropriate long-term solutions that maximize public benefit. These include:

  • Landward retreat of structures from dynamic shorelines


Where landward retreat is not feasible, beach nourishment* projects may be considered, on a case by case basis, as viable alternatives for short-term beach preservation.

Under no circumstances does the Surfrider Foundation support the installation of stabilization or sand retention structures along the coastline. Such structures can protect existing coastline development but have no place in beach preservation.

* For the purposes of this policy, 'beach nourishment' is defined as: the placement of clean sand of the appropriate composition and grain size on the beach or within the littoral environment. Under no circumstances is the incorporation of sand retention devices of any form to be construed as included within this definition.
Surfrider's State of the Beach Report provides an overview of our goals for managing seawalls and other shoreline structures, including specific examples from several states.

Legal Issues

Laws regulating construction of seawalls vary from jurisdiction to jurisdiction and state to state. In the US, seawall construction usually requires a permit from the local state's Coastal Zone Management agency, and may require additional review and permits from the federal government. For information about regulations regarding seawalls and other shoreline structures in a specific state, please visit the state reports page of the State of the Beach report, select your state, and then click on the link to the "Shoreline Structures" section.

Chapter Campaigns

Surfrider chapters around the country have and are fighting many battles involving seawalls. Here are links to information on a few of these campaigns:


Images

Photo Gallery of Seawalls

3D Photosynth of a seawall under construction in Carlsbad, CA

Video

Our colleagues at Surfrider Europe have put together a great video that covers not just seawalls, but coastal over-development in general and the resulting myriad adverse effects to our coastal environment.



References

  1. Mango, Cyril (2001), "The shoreline of Constantinople in the fourth century", in Necipoğlu, Nevra, Byzantine Constantinople: Monuments, Topography and Everyday Life, Istanbul: BRILL, pp. 19–28, ISBN 9004116257
  2. Bardill, Jonathan (2004), Brickstamps of Constantinople, Volume I: Text, Oxford University Press, ISBN 978-0-19-9255221



The Effects of Seawalls on the Beach: Part I, An Updated Literature Review. Nicholas C. Kraus and William G. McDougal. Journal of Coastal Research, Vol. 12, No. 3 (Summer, 1996), pp. 691-701

Abstract - A previous review by the first author of the literature on the effects of seawalls on the beach is extended to cover the period 1988 to the present. The review synthesizes knowledge on beach profile change, longshore sand transport, and scour in the vicinity of seawalls. Remarkable progress has been made since 1988, with new phenomena and observations reported, such as on longshore transport processes at walls. Some previous results and conclusions of the 1988 review have been cast into doubt, with example new results being that (1) wave reflection at walls may not be a significant contributor to profile change, and (2) scour at seawalls in the field may be more a product of longshore transport and return of overtopping water than a result of direct cross-shore wave action. The validity or usefulness of small-scale physical model tests is questioned. Conclusions and recommendations for future work are given. This paper is the first of a companion set of papers that investigate the effects of seawalls on the beach. The second paper presents a numerical model of cross-shore transport and beach profile change at seawalls that includes wave reflection, and it compares predictions to measurements made at the SUPERTANK project and to recent results found in the literature on scour at walls.

Ecological effects of coastal armoring on sandy beaches. Jenifer E. Dugan, David M. Hubbard, Iva´n F. Rodil, David L. Revell & Stephen Schroeter. Marine Ecology 29 (Suppl. 1) (2008) 160–170.

Abstract - Use of coastal armoring is expected to escalate in response to the combination of expanding human populations, beach erosion, and sea level rise along the coasts. To provide a conceptual framework, we developed hypotheses concerning the ecological effects of beach habitat loss associated with coastal armoring. As beaches narrow in response to armoring, dry upper intertidal zones should be lost disproportionately, reducing the habitat types available and the diversity and abundance of macroinvertebrates. Predators, such as shorebirds, could respond to a combination of (i) habitat loss; (ii) decreased accessibility at high tides; and (iii) reduced prey availability on armored beaches. To examine those predictions, zone widths and the distribution and abundance of macroinvertebrates and birds were compared on paired armored and unarmored segments of narrow bluff-backed beaches in southern California. Our results supported the predictions and revealed some unexpected effects of armoring on birds. Dry upper beach zones were lacking and mid-beach zones were narrower (>2 times) year-round on armored segments compared to adjacent unarmored segments. The abundance, biomass and size of upper intertidal macroinvertebrates were also significantly lower on armored segments. Shorebirds, most of which were foraging, responded predictably with significantly lower species richness (two times) and abundance (>3 times) on armored segments. Gulls and other birds (including seabirds), which use beaches primarily for roosting, were also significantly lower in abundance (>4 times and >7 times respectively) on armored segments, an important unexpected result. Given the accelerating pressures on sandy beaches from coastal development, erosion and rising sea levels, our results indicate that further investigation of ecological responses to coastal armoring is needed for the management and conservation of these ecosystems.

The Implications of Coastal Protection and Development on Surfing. Nicholas P. Corne. Journal of Coastal Research 25(2):427-434. 2009

Abstract - The impact of coastal protection on surfing resources is poorly understood and rarely quantified prior to construction. There is an increased requirement for surfing resources worldwide as participation levels in the sport grow. There is also an increased requirement for coastal protection as the occupancy in the coastal zone increases. This research paper takes the first steps towards a schematic categorization of the effect of coastal protection on surfing resources. To do this, we sourced the data through the global network of Surfrider Foundations via questionnaires. These questionnaires enquired about wave quality, crowd levels, stakeholder participation, and the economic importance of surfing to the local area before and after the construction of coastal protection.

The results show that of the 30 surfing resources surveyed, 18 experienced a reduction in wave quality and 12 showed an enhancement, or no change, in wave quality.

The paper provides an explanation of the results by proposing mechanisms of enhancement and reduction of wave quality after the construction of coastal protection. The conclusion states that coastal protection usually has an effect on the surfing resource that may be positive or negative in terms of the outcome on wave quality and crowd levels.

Rice, Tracy Monegan. 1999. Best Management Practices for Shoreline Stabilization to Avoid and Minimize Adverse Environmental Impacts, Prepared for the USFWS, Panama City Ecological Services Field Office.

Abstract - Shoreline stabilization projects can cause significant adverse environmental impacts to the coastal ecosystem. By incorporating conservation measures into a project during the planning, design, construction, and post-construction phases, many of the potential adverse environmental impacts can be avoided and minimized. This paper outlines best management practices (BMPs) that can be utilized as conservation measures to avoid, minimize, and mitigate adverse environmental impacts from shoreline stabilization projects. The first approach that best avoids and minimizes adverse environmental impacts from shoreline management is to "do nothing" and retreat roads and structures away from the shorelines as sea level rises and climate changes, and to prevent new development in naturally hazardous or migrating areas. Where shoreline stabilization is proposed, BMPs are presented in sections for dune, beach, nearshore, offshore, inlet and estuarine habitats, and an adaptive management framework is presented for project management (i.e., operations and maintenance) and issues relating to climate change and rising sea level. A glossary is included for key words and an extensive bibliography summarizes the scientific literature that provided scientific background and data in the development of these BMPs as conservation measures.

Links

Wikipedia Article on Seawalls

Ohio Department of Natural Resources Seawall Page



This article is part of a series on Shoreline Structures looking at types of structures commonly built along shorelines, and the policies, laws, and regulations which can affect where and under what conditions they are built.

For information about laws, policies and conditions impacting shoreline structures in a specific state, please visit Surfrider's State of the Beach report to find the State Report for that state, and click on the "Shoreline Structures" indicator link.